The present invention relates to optical switches and more particularly to bubble optical switches.
Optical communication networks use optical waveguides to transmit optical signals representing data. At various points along the network, optical switches are used to route optical signals from one waveguide to another. One type of optical switch uses fluids and vapor bubbles to switch optical signals. This type of switch is often referred to as a bubble switch. In this design, trenches are formed where the waveguides intersect and are filled with an index matching fluid, the index matching fluid having refractive index that is the same as the refractive index of the optical waveguides.
In an inactive state, a bubble switch includes a trench filled with index matching fluid. Because the index matching fluid has the same refractive index as the waveguide segments that intersect that the bubble switch, no switching is performed at the switch. That is, an optical signal from a first waveguide segment enters the fluid filled trench, passes straight through the fluid-filled trench, and enters a second waveguide segment. To activate the bubble switch, heat is applied to nucleate a bubble within the trench. The bubble displaces the fluid within the trench and fills the trench with vapor. The vapor has a refractive index that is close to one. Accordingly, the optical signal from the first waveguide is reflected at the wall of the vapor-filled trench and enters a third waveguide segment. To inactivate the bubble switch, heat is removed from the switch allowing the bubble to collapse and the index matching fluid to again fill the trench. The portion of the trench wherein the bubble displaces the index matching fluid is often referred to as a switching chamber.
For fast switch activation, the bubble must be nucleated quickly. This requires application of high temperature to the switch to quickly bring the index matching fluid to a boil to create vapor for the bubble. For example, for some index matching fluid,.temperatures of up to 225 degrees Celsius are required for nucleation. Once the bubble is nucleated, it can be maintained at a lower temperature such as 100 degrees Celsius. The high temperature required for nucleation stresses the bubble switch thus reduces the lifetime and reliability of the switch.
For fast switch deactivation, the bubble must be completely collapsed within the index matching fluid. However there is often air or other gaseous impurities in the fluid. These impurities must dissolve back into the fluid. The dissolution process is often inconsistent, leaving residual bubbles for 30 milliseconds or more. This causes disturbance in the path of optical signals and an inconsistent switch turn off time.
Consequently, there remains a need for an improved bubble optical switch that alleviates these shortcomings.
The need is met by the present invention. According to one aspect of the present invention, an optical switch includes a static bubble drum and a switching chamber. The static bubble drum is adapted to contain a static bubble. The switching chamber is adapted to allow the static bubble to expand into it from the static bubble drum.
According to another aspect of the present invention, each optical switch in a plurality of optical switches includes a static bubble drum and a switching chamber. The static bubble drum is adapted to contain a static bubble. The switching chamber is adapted to allow the static bubble to expand into it from the static bubble drum. Each optical switch in the plurality of optical switches also includes a heater that is proximal to the static bubble drum, switching chamber, or both.
According to yet another aspect of the present invention, a method for switching optical signal includes applying heat to a static bubble drum. The heat expands a static bubble from the drum into a switching chamber.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.